Blender I Hotkey not doing what it is supposed to
Blender uses several different 'modes' - the same keys sometimes work differently depending on the current mode. The mode menu is normally shown at the bottom of the 3DView.



Pressing I while in object mode will bring up the insert keyframe menu, unless you have specified a keying set for it to use automatically. When a keyframe is inserted you also get feedback in several areas - the timeline will show a yellow line on the frame that has a keyframe and numerical values will have a yellow background (this changes to green when you change frames)



If you are in edit mode of a mesh object then I will perform an inset on the selected part of the mesh.

CtrlI will invert the selection - both in object and edit mode.

Also blender uses "focus follows mouse" which is a bit different than most Mac and Windows users are used to, you need to have the mouse cursor over the part of the blender window that you want to perform the action, which for insert keyframe would be the 3DView.